Process of preparing calcium cyanamide



Patented Nov. 21, 1939 PROCESS or PREPARING CALCIUM CYANAMIDE ErnstWinter, Cologne- Braunsfeld, and ,Herbert Polack, KnapsaclmnearCologne-on-the-Rhine, Germany. assignors to A-ktiengcsellschaft fiirStickstoifdiinger,

Knapsack, near on-the-Rhine, Germany Cologne- No Drawing. ApplicationOctober 1,1937 Serial No. 166,714. In Germany October 2, 1936 1 Claim.

The present invention relates to a process of preparing calciumcyanamide in a revolving furnace at various degrees of dilution.

The action of the dilution upon the course of the reaction during thepreparation of calcium cyanamide is known and has been described forinstance in our copending United States application Serial No. 107,906filed October 27, 1936.

In all known processes the calcium carbide to be combined with nitrogenis mixed with an inert extender, preferably with calcium cyanamide, andthis mixture is introduced into the reaction furnace, or if the calciumcarbide and the diluent are separately introduced into the furnace thetwo components are mixed directly at the inlet. The diluent is mostlyadded to the carbide in the cold state. By cold state is meant that thediluent is cold relative to the temperature maintained in the furnace.

It is intended by the dilution to cause a mechanical separation of thecarbide particles from each other in order to prevent agglomeration ofthe particles at high and highest temperatures and to attain permanentlya sufficient cooling of the calcium carbide at these temperatures. Bythe absorption of heat the diluent added has to prevent an exceeding ofthe highest limit of temperature. This cooling by the diluent at thatpart of highest temperature, however, is only small. For, as the diluenthas always the same temperature as the reacting calcium carbide, it canabsorb heat only in a quantity corresponding to its further heating. Atthe peak of a vigorous reaction only a small rise of temperature of somedegrees may already cause the mass to sinter. In the case of this smallrange of temperature, however, the diluent is only capable of absorbinga small quantity of heat while the reaction or the quantity of heat setfree increases very rapidly at high temperatures. The cooling caused bythe diluent, therefore, is relatively the smallest where the increase ofthe evolution of heat is the greatest.

At the mouth of the furnace, however, the reaction occurs in a quitedifferent manner. Even when using hot diluents the temperature at themouth is always essentially lower than the highest temperature in thecentre of the furnace in accordance with the quantity of calcium carbideadded. The dilute carbide, therefore, has to run through a zone oftemperature of several hundred degrees until it reaches the completereaction speed and besides has to heat the diluent, too. The calciumcarbide and the diluent consume heat until the reaction heat of thecarbide rising with the temperature is suffi cient to elevate thetemperature of the mixture to a degree sufficient to promote theabsorption of nitrogen. It is evident that a pure calcium carbide reactsmore readily than a dilute carbide. The diluentthereing to use thisprocess for the working up of larger quantities of calcium carbide dustthe difficulties above referred to were observed.

Now We have found that the reaction conditions are quite different whenthe extender is added to the calcium carbide at that part of thereaction .zone in which already an excess of heat is produced. Accordingto this process the calcium carbide which may contain the usualcatalysts enters the furnace in the non-dilute state and is heated fromthe reaction zone by means of radiating heat. Only when the reactionproduces an excess of heat and the temperature tends to rise rapidly isthe extender added. The temperature and the quantity of diluent may bedetermined as desired so that the degree of dilution and the withdrawingof heat correspond to the reaction speed.

The extender may be added from the inlet or from the outlet side,preferably from both sides simultaneously. The extender may best beintroduced into the reaction zone by conveying it together with thenitrogen used according to the normal pneumatic conveying methods. Therange of the diluent is determined by the pressure of the nitrogen andby the direction of the end of the conveyor conduit projecting into thefurnace, If a calcium carbide is used for the absorption of nitrogenwhich also contains coarse constituents it is advisable to guide thefinal product over a dressing machine and to perform the dilution in thefurnace chiefly with the line constituents, be-

.15 cium carbide of a certain granular size. 'On trycause, owing to itslarger surface, the fine ma-

